Insect Transmitted Nematodes. Filarial worms Tissue dwelling parasites Order Spirurida Transmitted to definitive host through insect bite. Filarial Nematodes . Tissue-dwelling nematodes (not in digestive tract) Possess a unique life cycle stage – the microfilaria - between the egg and J 1
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Adults occur in the lymphatic vessels
Nocturnal periodicity of microfilariae
High levels of microfilaremia
Immune response down regulated
Sometimes no symptoms and no microfilaremia
Sometimes lymphatic inflammation and no microfilaremia
2. Inflammatory (Acute) Phase
Caused by antigens from adult worms
Inflammation due to bacterial infection
Adults interfere with lymph flow
3. Obstructive (Chronic) Phase
Obstructive phase photos
Causes Malayan filariasis
Distribution - Orient, South Pacific, and Southern Asia to India – overlaps with Wuchereria bancrofti - but does not occur in Africa or South America
Morphology and life cycle is similar to that of Wuchereria bancrofti
Pathology - Adults live in lymphatic vessels of the arms and legs and cause elephantiasis in these regions
Difference from Wuchereria?
Adult male: 6-12 inches long
Adult female: 12-16 inches long
Adults coiled in right side of dog heart
Unsheathed microfilaria in dog blood - DIAGNOSTIC
Causative agent of Onchocerciasis or River Blindness
DISTRIBUTION – Areas of Africa, Arabia, Guatemala, Mexico, Venezuela and Colombia
1. Adults live in coiled masses encapsulated under the skin.
2. Females produce microfilariae
- Microfilariae of Onchocerca NEVER invade the bloodstream.
3. Microfilariae in the skin are ingested by the black fly intermediate host, Simulium damnosum, when a blood meal is taken.
4. Parasites develop to J3’s in the musculature of the black fly and migrate to the mouthparts.
5. J3’s are inoculated into the skin when black fly bites.
Adults mature in a year within subcutaneous nodules.
Microscopic section showing adults and scar tissue reaction around them forming the nodule
Skin nodule cut open to reveal adults coiled together
Unsheathed microfilariae occur in the skin, never the bloodsteam
ADULTS cause onchocercomas
Nodules are about ½ -1 inch in diameter.
Nodules are relatively benign and cause only some disfigurement.
2. Microfilariae in skin cont:
- in parts of Africa, the skin of the scrotum and inguinal area loses its elasticity causing hanging groin!
3. Microfilariae invade the eye
-blindness occur as microfilariae die in the eye
- fibrosis causes clouding of cornea and aqueous and vitreous humors resulting in blindness
- fibrosis of the eye is a slow development and most affected persons are adults over 40 years old!
In many parts of Africa, the sighted young are responsible for leading the older blind adults.